1. Field of the Invention
The present invention concerns a single-piece snap hinge closure of plastic with a lower part and a cap, whereby each part has a casing wall. In the closed condition of the closure, these casing walls stand vertically above one another at equal elevation. The lower part is connected with the cap by means of at least one film hinge as well as by means of two tension bands positioned on each side of the film hinge, which bands, in the closed condition of the closure, are extended.
2. Description of the Prior Art
A snap hinge closure of the general type already stated is known, for example, from European Pat. No. 0 147 423. The tension bands according to the prior art patent are generally connected to attachments, which are placed on the external casing surface and lie in a plane which intersects the plastic closure in the manner of a secant. These closures have proven to be most superior, considered from the viewpoint of the manner of their operation, strength and closing force. What has been found defective in the marketplace, however, has been, above all else, their aesthetic appearance, as well as the possibility of working with the closures in bottling stations. The protruding tension bands provided a genuine cause for obstructions on conveyor belts.
One solution to the second problem stated is represented in European Pat. No. 056 469. In this case, instead of tension bands, work is carried out with intermediate elements positioned laterally to the film hinge joint, which are thick-walled and are connected with the lower part or the cap by means of film hinges. The force necessary for the snapping effect to take place is not formed here by the longitudinal expansion of the intermediate elements, but rather through the re-forming force of the intermediate elements which are arch-shaped. The tension forces arising during the opening and closing of the closure run through the film hinges, by which the intermediate elements are connected with the cap or the lower part. The film hinge forming the swivel axis is compressed upon opening the closure. While the compression of a film hinge is non-problematic, tension forces represent a great danger to the film hinge. If the tension forces proceed precisely in the direction perpendicular to the axis of the film hinge, then the resistance force is still relatively great. In one oblique position of the film hinge, as European Pat. No. 056 469 claims, however, the stated correct force effect is not ensured. The result is that, on the sides of the film hinges, an excess expansion appears with the notch effect, and the film hinges tear.